The terminal selenido complexes W(PMe3)4(Se)H2 and trans-W(PMe3)4(Se)2 are formed sequentially by the reaction of W(PMe3)4(eta2-CH2PMe2)H with H2Se. Dissociation of PMe3 from W(PMe3)4(Se)2 is facile, and treatment with Bu(t)NC and aldehydes yields the derivatives trans,trans,trans-W(PMe3)2-(CNBu(t))2(Se)2 and W(PMe3)2(Se)2(eta2-OCHR) (R = H, Ph), respectively. The series of terminal selenido complexes have been studied by X-ray diffraction and Se-77 NMR spectroscopy.